This invention relates to formation of copper thin films, and specifically to the formation of a copper thin film on a nitride-based substrate using a volatile precursor and CVD.
Because of the low electrical resistivity, xcx9c1.7 xcexcxcexa9-cm, and high resistance to electromigration, the use of CVD to form copper thin films has gained much attention. Copper thin film is considered to be ideal for use as metal interconnection material in IC devices.
The techniques for CVD of copper thin films requires the use of a stable and volatile precursor, preferably in liquid form. From a commercial standpoint, the precursor cost must be reasonable. The resulting thin film must have good adhesive properties to metal-nitride coated substrates, low resistivity, i.e.  less than 1.8 xcexcxcexa9-cm, excellent conformity to surface structures and irregularities, and good electromigration resistance. In CVD processing, the copper precursor must have not only a high enough vapor pressure to maintain a reasonable deposition rate, it must also be stable at the deposition temperature without any decomposition in the CVD liquid delivery line or vaporizer.
Copper metal thin films may be prepared via CVD by using any of a number of copper precursors, such as Cu(C5H5)(PR3), where R=methyl, ethyl, or butyl, as disclosed by Beach et al., in Chem. Mater., Vol. 2, pp. 216-219 (1990). Hampden-Smith et al. achieved similar results using (tert-BuO)Cu(PMe3), Chem. Mater., Vol. 2, p 636 (1990). The previously described thin films, however, contain sufficient contaminants of carbon and phosphorous to preclude use of the resulting thin film as interconnectors in microprocessors.
The studies of copper precursors in the early 1990""s concentrated on the evaluation of a series of copper(I) fluorinated xcex2-diketonate complexes, have subsequently been proven to be acceptable sources for use in CVD of copper metal thin films. Copper(I) fluorinated xcex2-diketonate complexes were first synthesized by Doyle, U.S. Pat. No. 4,385,005, for Process for separating unsaturated hydrocarbons using copper or silver complexes with fluorinated diketonates, granted May 24, 1983, and U.S. Pat. No. 4,425,281, for Copper or silver complexes with fluorinated diketones and unsaturated ligands, granted Jan. 10, 1984, which describe the synthesis method and application in the separation of unsaturated organic hydrocarbons. Doyle et al., Organometallics, Vol. 4, p. 830 (1985)
U.S. Pat. No. 5,096,737 to Baum et al., for Ligand stabilized +1 metal xcex2-diketonate coordination complexes and their use in chemical vapor deposition of metal thin films, granted Mar. 17, 1992, describes the use of copper(I) fluorinated xcex2-diketonate complexes as copper precursors for CVD copper thin film preparation. Subsequent work described the use of Cu(hfac)(CH3Cxe2x89xa1CCH3), where hfac=hexafluoroacetylacetonate, as disclosed by Baum et al., Chem Mater, Vol. 4, p. 365 (1992), and Baum et al., J. Electrochem. Soc., 1993, Vol. 140, No. 1., 154-158 (1993). Copper thin films have been prepared via CVD using these precursors.
Other potential precursors, including 1,5-dimethyl 1,5-cyclooctadiene copper(I) hexafluoroacetylacetonate mixed with 1,6-dimethyl 1,5-cyclooctadiene copper(I) hexafluoroacetylacetonate ((DMCOD)Cu(hfac) and hexyne copper(I) hexafluoroacetylacetonate ((HYN)Cu(hfac) have been extensively evaluated. The copper thin films deposited using (DMCOD)Cu(hfac) demonstrate good adhesive properties to metal and metal nitride substrates, however, they have a resistivity on the order of 2.5 xcexcxcexa9-cm and also have a low deposition rate. (HYN)Cu(hfac) suffers from poor adhesion to a TiN substrate, and has a resistivity on the order of 2.1 xcexcxcexa9-cm, which is unacceptable.
Another compound, butyne copper(I)(hfac), ((BUY)Cu(hfac), provides a copper thin film having a low resistivity of about 1.93 xcexcxcexa9-cm, however, the thin film demonstrates poor adhesive properties, the precursor is relatively expensive and is a solid at room temperature.
The provision of Cu(hfac)(TMVS) precursor, where TMVS=trimethylvinylsilane, as disclosed by Norman et al., Journal de Physique IV, Vol. 1., C2-271-278, September 1991, and U.S. Pat. No. 5,085,731 for Volatile liquid precursors for the chemical vapor deposition of copper, granted Feb. 4, 1992, resulted in copper thin films having improved properties. Copper thin films deposited using liquid Cu(hfac)(TMVS) have low resistivites and are reasonably adhesive to substrates. This particular precursor has been used for copper thin film formation by CVD for some time, however, the precursor still exhibits some drawbacks, such as a lack of stability, less than desirable adhesion, and excessive cost, as the TMVS stabilizer is an expensive compound. The foregoing have reported the deposition of pure copper thin films in laboratory processes.
A method for chemical vapor deposition of copper metal thin film on a substrate includes heating a substrate onto which the copper metal thin film is to be deposited in a chemical vapor deposition chamber; vaporizing a precursor containing the copper metal, wherein the precursor is a compound of (xcex1-methylstyrene)Cu(I)(hfac), where hfac is hexafluoroacetylacetonate, and (hfac)Cu(I)L, where L is an alkene; introducing the vaporized precursor into the chemical vapor deposition chamber adjacent the heated substrate; and condensing the vaporized precursor onto the substrate thereby depositing copper metal onto the substrate.
A copper metal precursor for use in the chemical vapor deposition of a copper metal thin film is a compound of (xcex1-methylstyrene)Cu(I)(hfac), where hfac is hexafluoroacetylacetonate, and (hfac)Cu(I)L, where L is an alkene taken from the group of alkenes consisting of 1-pentene, 1-hexene and trimethylvinylsilane.
It is an object of the invention to provide a copper thin film CVD precursor which is stable, liquid at ambient temperatures, and is relatively inexpensive.
Another object of the invention is to provide a copper thin film CVD precursor which results in a copper thin film having good adhesive properties to underlying substrates, particularly those having nitride components.
A further object of the invention is to provide a copper thin film CVD precursor which results in a copper thin film having desirable electrical properties.
This summary and objectives of the invention are provided to enable quick comprehension of the nature of the invention. A more thorough understanding of the invention may be obtained by reference to the following detailed description of the preferred embodiment of the invention in connection with the drawings.